This invention relates to an automatic shoe clearance adjustment device for a drum brake equipped with an over-adjustment prevention mechanism for a clearance between a brake drum and a brake shoe.
This type of automatic shoe clearance adjustment device is disclosed in the Japanese Patent Publication Number H2-15737. This device is characterized in that an adjustment lever is pivotally mounted on one brake shoe; an extended portion is integrally formed as an extended end of the adjustment lever; an end of the extended portion is arranged to be located between an end part of a piston of a wheel cylinder and an end part of a shoe web of the brake shoe; when an actuating force of the piston reaches a predetermined value, the adjustment lever rotation is restricted, upon a lining of the brake shoe contacting the brake drum, to cease the automatic shoe clearance adjustment.
In this device, because of an uneven manufacturing tolerance of the brake shoe and the adjustment lever, there needs to be a gap between the end of the shoe web and the end of the extended portion of the adjustment lever. This gap can cause a deformation and breakage at the extended portion when in a high pressure braking application. In addition, since braking is a very frequent action, the pivot section of the adjustment lever becomes worn out which may inhibit the adjustment lever rotation.
This invention was made to mainly improve the above-mentioned points, and to that end, it is an object of this invention to provide an automatic shoe clearance adjustment device for a drum brake designed to improve its durability by eliminating the gap resulting from manufacturing tolerances.
It is another aspect of this invention to provide an automatic shoe clearance adjustment device for a drum brake which ensures a long-term reliable shoe clearance.
This invention is an automatic shoe clearance adjustment device for a drum brake, comprising: a pair of brake shoes slidably mounted on a back plate; an extendible strut restricting the initial position of the pair of brake shoes; an adjustment lever pivotally supported at one of the brake shoes, the adjustment lever being rotatable in response to an excessive opening of the brake shoes upon operation of a service brake actuator and the adjustment lever having an extended portion integrally formed as an extended end thereof, the extended portion being arranged between the abutment surfaces at the actuating force transmitting section through which the actuating force of the service brake actuator is transmitted to the one of the brake shoes, and the adjustment lever being adapted to stop rotating when the actuating force of the service brake actuator reaches a predetermined value; wherein the adjustment lever is pivotally supported with a capacity of making a rotation relative to the one of the brake shoes and a capacity of making a relative slide in approximately the same direction in which the service brake actuator operates.
This invention still is an automatic shoe clearance adjustment device as claimed above, wherein: a projection is formed either on the adjustment lever or on the one of the brake shoes; and the projection is pivotally supported at a long hole formed either on the other one of the adjustment lever or the one of the brake shoes on which the projection is not formed.
This invention still further is an automatic shoe clearance adjustment device as claimed above, wherein the projection is a protuberance integrally formed with the adjustment lever or the one of the brake shoes by deep drawing by pressing.
This invention still further is an automatic shoe clearance adjustment device for a drum brake, comprising: a single brake shoe slidably mounted on a back plate; an extendible strut restricting the initial position of the brake shoe; a link engaging, with a capacity of depressing, a central region of the brake shoe; and adjustment lever pivotally supported at the link, the adjustment lever being rotatable in response to an excessive opening of the link upon operation of a service brake actuator and the adjustment lever having an extended portion integrally formed as an extended end thereof, the extended portion being arranged between the abutment surfaces at the actuating force transmitting section through which the actuating force of the service brake actuator is transmitted to the link; and the adjustment lever being adapted to stop rotating when the actuating force of the service brake actuator reaches a predetermined value; wherein the adjustment lever is pivotally supported with a capacity of making a rotation relative to the link and a capacity of making a relative slide in approximately the same direction in which the service brake actuator operates.
This invention still further is an automatic shoe clearance adjustment device as claimed above, wherein a projection is formed either on the adjustment lever or on the link and the projection is pivotally supported at a long hole formed either on the adjustment lever or said link on which the projection is not formed.
This invention still further is an automatic shoe clearance adjustment device as claimed above, wherein the projection is a protuberance integrally formed with the adjustment lever or the link by deep drawing by pressing.
This invention still further is an automatic shoe clearance adjustment device as claimed above, wherein both abutment surfaces of the extended portion of the adjustment lever and the brake shoe or the link are formed in a circular shape and a radius of curvature of said abutment surface of said adjustment lever is set to be larger than that of said abutment surface of the brake shoe or said link.
This invention yet further is an automatic shoe clearance adjustment device as claimed above, wherein
an end portion of the extended portion of adjustment lever is bent outward, and the bent portion is arranged to face the peripheral surface of a service brake actuator piston (151,51) at the back plate side.